why does photoshop cs5 load so slow with avast6?

Hi

i 'm using avast6 free , and i’m testing thinking about the purchase

well my photoshop is legit , updated ,and i run under w7

well with avira , nod32 photoshop start as soon as i click on it

with avast it takes some seconds ???

yes yes i let avast create the cache with a full system scan and reboot

all my tests are made with a fresh install of w7

i did notice avast is amazing fast when i run a program , but become slow the the program is about 30mb…

thanks